Papers by Keyword: MgH2

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Authors: Jian Gang Niu, Fei Xie, Ke Jun Jia, Li Guan, Xiao Ping Dong
Abstract: First-principles calculations were performed to study the relative stabilities of MgH2 and Mg7XH16(X=Nb,V,Ti).The calculated results show that MgH2 has the higher stability than Mg7XH16. The density of states of MgH2 and Mg7XH16 were obtained and analysized. It shows that the extinction of the gap at 0~4eV interval , the increment of N(EF) and the weakening of Mg-H bonds impaired the stability of Mg7XH16.
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Authors: Efi Hadjixenophontos, Lukas Michalek, Andreas Weigel, Guido Schmitz
Abstract: The diffusion mechanism of H in metals and metal hydrides is studied particularly at high H2 pressures. Thin films of Mg and Ti offer a convenient tool to quantify the atomic transport. We show how different parameters of hydrogenation affect the kinetics. At 200°C, the Pd-Mg interface is predominant and a linear regime of hydrogenation is observed, whereas at 300°C a parabolic regime is detected. In Mg, the hydride forms from the surface to the substrate whereas in Ti growth of TiH2 starts from the substrate. A linear kinetics is seen during hydrogenation of Ti films, which is due to the oxide layer on top, measured to be about 10nm thick. In the studied high pressure regime, the hydrogenation is not pressure dependent any more. Quantitative calculation of the growth rate and the diffusion coefficient of H in the hydrides is presented.
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Authors: Xiao Dong Luo, Jing Zhang, Hao Liu
Abstract: Magnesium hydride is considered as one of the most interesting alternatives for the reversible storage of hydrogen. In this study,The feasibility and reaction process of different materials(Mg and pretreated Al powders(mainly composed of Al and Ni))were discussed and investigated by thermodynamic calculation. The effects of material proportioning, mill time, mill energy density were also investigated by XRD analysis and TG-DSC technique, and analyzed the essence mechanism. The results show that nano-sized MgH2 and Mg(AlH4)2 could be directly synthesized by pure Mg and pretreated Al powder, The product composite hydrides release 2.7wt% H2 through multi-step decompositions, of which the starting endothermic peaks are as low as 265°C.
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Authors: De Hua Zhang, Wen Hao Fan, Feng Zhang, Shao Ping Chen, Qing Sen Meng
Abstract: In the present study, Mg2Si nanoparticles of high purity were successfully synthesized through low-temperature reaction by using MgH2 and Si powders as rawmaterials. The size of Mg2Si particles is about 50nm. The bulk nanocomposites xSiO2/Mg2Si0.8Sn0.2(x = 0, 0.1, 1 and 2wt. %) were followed by field-Activated and pressure-assisted synthesis (FAPAS). The effects of SiO2 addition on the microstructure and thermoelectric properties of Mg2Si0.8Sn0.2 were studied. The field emission scanning electron microscopy shows that the nanometer-sized SiO2 particles disperse homogeneously in Mg2Si0.8Sn0.2 matrix. Among all of the samples, 1wt. % SiO2/Mg2Si0.8Sn0.2 exhibits the best figure of merit (ZT = 0.25 at 573 K), which is 24% higher than that of the sample without SiO2, indicating that the thermoelectric properties of Mg2Si0.8Sn0.2 can be enhanced effectively by the dispersion of nanometer-sized SiO2.
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Authors: Ricardo Mendes Leal Neto, Rafael de Araújo Silva, Ricardo Floriano, Graziele Cristina Seco Coutinho, Railson Bolsoni Falcão, Daniel Rodrigo Leiva, Walter José Botta Filho
Abstract: The aim of this work is to investigate the influence of some processes variables on the microstructure and hydrogen absorption kinetics of MgH2 - X wt.% TiFe composites. Samples were synthesized by high-energy ball milling in a planetary (X = 40, 50, 60) and shaker mill (X = 40) under high-purity argon atmosphere. Commercial MgH2 instead of Mg powder was used in order to reduce adherence on the vial and balls. TiFe powder was previously produced by ball milling a mixture of TiH2 and Fe powders followed by a reaction synthesis at 600oC. Milled composites samples were characterized by XRD and SEM analysis. Milling time was preliminary investigated (X = 40) in the planetary ball mill (6 to 36h). TiFe particle size reduction was shown to be difficult since they are surrounded by MgH2 matrix. Strong particle reduction was obtained by using a shaker mill only for 2 hours and adding cyclohexane as process control agent. No reaction between MgH2 and TiFe compound was observed in any milled sample. Hydrogen absorption kinetics measurements of the as-milled samples were conducted on an Sieverts' type apparatus at room temperature after hydrogen desorption at 350oC under vacuum. The best hydrogen kinetics (3 wt% at the first hour) was attained by the planetary milled sample (36 h). Higher hydrogen capacity was observed for the sample milled in the shaker mill (4.0 wt.%), but only after 13h.
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Authors: Chan Yeol Seo, Xiao Dong Wu, Kiyonori Suzuki
Abstract: It is well known that catalytic additives and mechanical milling are effective in improving hydrogen desorption kinetics of MgH2. In this study, the effect of catalytic additives including BaCa1-xNdxO3-δ (BCN) on the desorption behavior of MgH2 was investigated. It was found that BCN can improve the desorption kinetics, but not as effective as other known additives such as Nb2O5. The effect of milling temperature was also studied. It was found that the cryogenic milling is not as effective as room temperature milling primarily due to the inhomogeneous particle size distribution.
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